Particulate solids, such as, microbial, animal or plant cells or their components attached to artificial carriers, or nutrient substrates, are involved in many useful and potentially useful bioconversion or biotransformation processes. In carrying out such processes, it is often essential to contact the solid particles with a liquid phase to permit biochemical reactions involving components contained in the solids and in the liquid phase to occur. It also may be essential for a gas solute, for example, oxygen, to be transferred from a gas phase, such as, air, into the liquid medium. In addition, the processes may need to be carried out under mild conditions of mixing and agitation in order to avoid deleterious effects, such as, cellular damage or excessive use of energy for mixing and/or aeration.
In the prior art, such bioconversion or biotransformation processes are accomplished in reactor devices which normally employ simple mechanically-stirred or pneumatically-stirred vessels. These prior art devices, however, suffer from one or more of several drawbacks, including the accumulation of particulate solids in unmixed stagnant zones in the vessel, the growth of organisms in crevices and other stagnant-zone or poorly mixed regions of the vessel, the development of foam at the top of the aerated medium, and damage and destruction of biological cells by higher shear and excessive use of energy for mixing and/or aeration.